Pore-Scale Modeling of the Fuel Cell Catalyst Layer: The Role of Nafion Thin Films

Abstract

In this work, a multiphysics pore-scale model of electrochemical reactive transport inside a fuel cell catalyst layer (CL) is presented and is used to elucidate the role of Nafion thin films on the overall performance of the CL. One of the main challenges of modeling transport in CL is the hierarchy of length scales and the multiphysics nature of transport. Consequently, traditional continuum methods, in which volume-averaged quantities are used to encapsulate the microstructural features, cannot give a clear picture of the multiphysics transport processes inside the CL. Alternatively, pore-scale methods, which take into account the true geometry down to the pore level, are suited to capture these processes for such systems. Previously, researchers have mainly employed direct numerical simulation (DNS) techniques for pore-scale modeling of the CL. While these techniques are highly accurate, they are very computationally expensive. This limits the domain size that can be simulated in a reasonable time. In this work, pore network modeling, a computationally cheap technique to simulate pore-scale transport, is used to study transport in the CL. Using this approach, we were able to speed up the simulation runtime up to 20-50x compared to DNS. Consequently, simulation of much larger domains of the CL was made possible, leading to more representative results. Finally, the developed multiphysics pore-scale model was used to study the role of Nafion thin films on the overall performance of the CL. It is notable that the network approach was only applied to the void phase, and the Nafion region was resolved using DNS. Therefore, yet further speed up can potentially be obtained by applying the network approach to the Nafion phase.